<template>
    <div>
        <router-link 
            tag="div" 
            to="/" 
            class="header-abs"
            v-show="showAbs"
        >
            <div class="iconfont header-abs-back">&#xe624;</div>
        </router-link>
        <div 
            class="header-fixed" 
            v-show="!showAbs"
            :style="opacityStyle"
        >
            景点详情
            <router-link to="/">
                <div class="iconfont header-fixed-back">&#xe624;</div>
            </router-link>
        </div>   
    </div>
</template>


<script>    
export default {
    name:"DetailHeader",
    data(){
        return {
            showAbs: true,
            opacityStyle:{
                opacity:0
            }
        }
    },
    methods:{
        handleScroll(){
            const top = document.documentElement.scrollTop
            if( top>60 ){
                //当滚动条的值（top）去到140时候，opacity的值为最大值，
                let opacity = top /140
                //如果opacity的值大于1，则让这个值为1
                opacity = opacity > 1 ? 1: opacity
                this.opacityStyle={ opacity}
                this.showAbs = false
            }else{
                this.showAbs = true
            }
        }
    },
    activated () {
        window.addEventListener('scroll',this.handleScroll)
    },
    deactivated(){
        //window.addEventListener的事件为全局事件，需要在切换页面刷新时使用生命周期deactivated删除全局事件
        window.removeEventListener('scroll',this.handleScroll)
    }
}
</script>


<style lang="stylus"  scoped>
    @import '~styles/varibles.styl'
    .header-abs
        position: absolute 
        left: .2rem
        top: .2rem
        width: .8rem
        height: .8rem
        line-height: .8rem
        border-radius: .4rem
        text-align:center
        background: rgba(0,0,0,.8)
        .header-abs-back
            color: #ffffff
            font-size: .4rem
    .header-fixed
        position: fixed
        top: 0
        left: 0
        right: 0
        overflow: hidden
        height: $headerHeight
        line-height: $headerHeight
        text-align: center
        color: #fff
        background: $bgColor
        font-size: .32rem
        z-index: 2
        .header-fixed-back
            position: absolute
            top: 0
            left: 0
            width: .64rem
            text-align: center
            font-size: .4rem
            color: #fff
</style>
